1. Field of the Invention
The present invention relates to an image projecting apparatus for enlargingly projecting an image formed by an optical modulating device such as a liquid crystal panel on a display surface such as a screen.
2. Related Background Art
An optical system for a liquid crystal projector using a reflection type liquid crystal device is proposed in Japanese Patent Application Laid-Open No. 6-265842. This optical system is known as the Schlieren optical system. The prior art optical system will be explained with reference to FIG. 1.
Referring to FIG. 1, light beams from a light source 1 are substantially collimated by a paraboloidal reflector 2 (a paraboloidal mirror) and, after being reflected by a mirror 3, a light source image is formed in the vicinity of a reflecting mirror 7 disposed in a position of an aperture stop 13 of a projection lens 14. The light beams reflected by the reflecting mirror 7 outgo toward a plano-convex lens 8 and become parallel light beams through the plano-convex lens 8. The light beams are then separated into the light beams of three colors R, G, B by a cross dichroic prism 9, on the light beams in the respective colors (wavelength bands) illuminate reflection type liquid crystal display panels 10, 11, 12.
The respective color light beams modulated by the reflection type liquid crystal panels 10, 11, 12 are color-synthesized as the reflected light beams having image information again by the cross dichroic prism 9, and converged by the plano-convex lens 8. Then, the converged light beams pass through an aperture of the aperture stop 13 and are projected onto a screen 15 via the projection lens 14.
The liquid crystal panels 10, 11, 12, within which polymer dispersion type liquid crystals are sealed, control directions of liquid crystal particles by electric fields so as to reflect incident light beams by becoming transparent when displaying a white level and scatter the incident light beams when displaying a black level. The light beams, which have been reflected by the liquid crystal panel and color-synthesized by the cross dichroic prism 9, are converged in the vicinity of the aperture stop 13 of the projection lens 14 by the plano-convex lens 8. Most of the light beams reflected by the liquid crystals pass through the aperture of the aperture stop 13. After traveling through the projection lens 14, they are displayed as the white level on the screen 15. However, an extremely small quantity of the whole light beams scatter by the liquid crystals just pass through the aperture of the aperture stop 13 and therefore appear as the black level on the screen 15.
According to the prior art, however, there arises a problem in which a color ununiformity and a luminance ununiformity of the light source occur on the screen. Further, the light source image formed by the reflector exhibits a rotation symmetry, and hence there might be a large loss of light quantity when illuminating a rectangular liquid crystal panel, resulting in such a problem that the luminance on the screen decreases.
It can be considered that an integrator is introduced in order to solve this problem, however, the light source image formed at the aperture of the aperture stop 13 of the projection lens 14 is destined to be enlarged only by simply disposing the integrator, and the quantity of the light passing through the aperture of the aperture stop 13 decreases when displaying the white level. Further, when aperture of the stop is widened to prevent the reduction in the optical quantity, the contrast is destined to be declined. Thus, the integrator effective for decreasing the color ununiformity and the luminance ununiformity on the screen is no good in terms of compatibility with the Schlieren optical system.